1. Field Of The Invention
The invention relates to sinterable zirconium oxide powder and a process of preparing such sinterable zirconium oxide powder.
2. Background Art
To produce ceramic made of partially stabilized (PSZ) or tetragonal (TZP) zirconium oxide, powders made of zirconium dioxide with stabilizer and/or alloy additives are needed that contain these additives in as homogeneous a distribution as possible. This can be achieved, for example, in that from an aqueous zirconium salt solution, which additionally contains salts of the desired alloy elements, the hydroxides or hydrated oxides of the zirconium and of the alloy elements are precipitated together, dried and calcined. Here, usual above all as a stabilizer additive is yttrium oxide that is homogeneously dissolved in the powder obtainable in the way described above and that is usually present in a concentration of about 3 mol percent (about 5 to 6 percent by weight). It is true that the ceramic produced from this powder exhibits good mechanical properties at normal temperature but shows, upon being at a temperature between 100.degree. and 400.degree. C. for a prolonged time, a great decrease in strength by conversion into the monoclinic modification. Therefore, it is desirable to have sinterable zirconium oxide powders available that contain other stabilizer or alloy elements that prevent or delay this undesired strength decrease.
But the use of the process of coprecipitation from aqueous solutions was not previously possible for several potential stabilizer or alloy elements because the available salts of these stabilizer or alloy elements were not stable enough in aqueous solution. Especially TiCl.sub.4 and TaCl.sub.5, which hydrolyze immediately with water are noted. This difficulty was circumvented previously by using, instead of the halides, the corresponding alkoxides which can be hydrolyzed in a controllable way. But because of the considerably higher prices of these alkoxides compared to the chlorides, this method has the disadvantage of high costs.